John was cast into prison - For an account of the imprisonment of John see Matthew 14:1-13.

He departed into Galilee - See Matthew 2:22. The reasons why Jesus then went into Galilee were probably:

1. Because the attention of the people had been much excited by John's preaching, and things seemed to be favorable for success in his own ministry.

2. It appeared desirable to have some one to second John in the work of reformation.

3. It was less dangerous for him to commence his labors there than near Jerusalem. Judea was under the dominion of the scribes, and Pharisees, and priests. They would naturally look with envy on any one who set himself up for a public teacher, and who should attract much attention there. It was important, therefore, that the work of Jesus should begin in Galilee, and become somewhat established and known before he went to Jerusalem.

The Springing of the Great Light'Now when Jesus had heard that John was cast into prison, He departed into Galilee; 13. And leaving Nazareth, He came and dwelt in Capernaum, which is upon the sea coast, in the borders of Zabulon and Nephthalim: 14. That it might be fulfilled which was spoken by Esaias the prophet, saying, 15. The land of Zabulon, and the land of Nephthalim, by the way of the sea, beyond Jordan, Galilee of the Gentiles; 16. The people which sat in darkness saw great light; and to them which sat in the region and …Alexander Maclaren—Expositions of Holy Scripture

July the Thirteenth Plain Glass"They were fishers." --MATTHEW iv. 12-22. And so our Lord went first to the fishing-boats and not to the schools. Learning is apt to be proud and aggressive, and hostile to the simplicities of the Spirit. There is nothing like plain glass for letting in the light! And our Lord wanted transparent media, and so He went to the simple fishermen on the beach. "God hath chosen the foolish things of the world." And by choosing labouring men our Master glorified labour. He Himself had worn the workman's …John Henry Jowett—My Daily Meditation for the Circling Year

Jesus Sets Out from Judæa for Galilee. Subdivision A. Reasons for Retiring to Galilee. ^A Matt. IV. 12; ^B Mark I. 14; ^C Luke III. 19, 20; ^D John IV. 1-4. ^c 19 but Herod the tetrarch [son of Herod the Great, and tetrarch, or governor, of Galilee], being reproved by him [that is, by John the Baptist] for Herodias his brother's wife, and for all the evil things which Herod had done [A full account of the sin of Herod and persecution of John will be found at Matt. xiv. 1-12 and Mark vi. 14-29. John had spoken the truth to Herod as fearlessly …J. W. McGarvey—The Four-Fold Gospel

General Account of Jesus' Teaching. ^A Matt. IV. 17; ^B Mark I. 14, 15; ^C Luke IV. 14, 15. ^a 17 From that time Jesus began to preach [The time here indicated is that of John the Baptist's imprisonment and Jesus' return to Galilee. This time marked a new period in the public ministry of Jesus. Hitherto he had taught, but he now began to preach. When the voice of his messenger, John, was silenced, the King became his own herald. Paul quoted the Greeks as saying that preaching was "foolishness," but following the example here set by …J. W. McGarvey—The Four-Fold Gospel

Cross References

Matthew 11:2 Now when John, while imprisoned, heard of the works of Christ, he sent word by his disciples

Matthew 14:3 For when Herod had John arrested, he bound him and put him in prison because of Herodias, the wife of his brother Philip.

Mark 1:14 Now after John had been taken into custody, Jesus came into Galilee, preaching the gospel of God,

Luke 3:20 Herod also added this to them all: he locked John up in prison.

Luke 4:14 And Jesus returned to Galilee in the power of the Spirit, and news about Him spread through all the surrounding district.

Luke 23:5 But they kept on insisting, saying, "He stirs up the people, teaching all over Judea, starting from Galilee even as far as this place."

John 1:43 The next day He purposed to go into Galilee, and He found Philip. And Jesus said to him, "Follow Me."